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ARCH. No. 271,344.

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UNITED A STATES PATENT EEreE.

rHoMAs J. LovEcaovE, or PHiLAnELPHiA, PENNsvLvANiAi ARCH.

SPECIFICATION forming part of Letters Patht No. 271,344, dated January 30, 183.

(No model.)

To all whom it may concern:

Be it known that I, THOMAS J.LOVEGROVE, ofthe city and county of Philadelphia, and State of Pennsylvania, have invented certain new and useful Improvements in the construction of Arches, of which the following is a specification.

My invention relates to an improved method and devi'ces whereby arches for conduits, sewers, bridges, and other purposes may be constructed of maximum strength with the minimum of labor and material.

In every arch with which I have been heretofore acquainted the tendency is to the production of a number ot' foree-resultants between the crown and the skewbacks--that is to say, the direction of the lines of force or thrust which tend to destroy the structure is tangential to the curve ofthe arch. Consequently, in order to equalize the strength ot' the latter, it has been necessary to place a surplus of material of which it is constructed out of line, so that the true line of "equipollence'shall practically lie between theextrados and the intrados of the voussoirs.

lIn technical works, and particularly in those relating to the construction ot' arches and bridges, it. is common to see the term equilibrium applied to -the curve of the arch; but in all cases it is used simply in an approximate sense, as heretofore it has been impossible to accurately construct an equilibriumarch supporting an unequal load. It' we con sider the catenary inverted it is not a true equilibrium-arch, unless we imagine the cable Awithout weight, and the greater the weight the greater will be the discrepancy between the arch obtained and the true equilibriumarch. Heretolore the nearest method for approximating an equilibrium -arch for an uueven load was by considering a chain or cable hung from two points, with the variable loads hung from said cable along its length, and after ascertaining the curve produced the same was inverted and called the equilibriu m-arch 7 for that unequallydistributed load; but this was only approximate, as where the greatest tension was now we would have the greatest compression, and it is utterly impossible to cause all of the resultant forces to pass down through the skewbacks. The formulas heretofore used for the mathematical calculation and demonstration of the equilibriumarch are based upon the above facts.

An arch constructed upon the system hereinafter explained has substantially, both theoretically and practically, but two grand resultants-one to the right, the other to the left, from keystone to skewback. Such. arch carries its load as absolutely as a plumb column supports the weight upon it. An arch constructed on anyother principle has its counterpart in a bent column, the tendency of which is to spring ont from the pressure of the superincumbent load. Au arch constructed upon the principles now to be set forth enables me to use a movable templet merely, instead of the usual temporary center or support.

I shall now proceed to describe the mode of carrying out my invention, reference being had, as may be necessary, to the accompanying drawings, of which- Figure 1 is a perspective view of a conduitarch in process of construction with movable templet. Fig. 2 is an end view thereof, the arch being in section made adjacent to one'of the re-enforcing ribs, hereinafter mentioned. Fig. 3 is for reference in illustrating my system for determining the proper form of the arch or arches to be constructed. Fig. 4 represents the mode of applying my invention in the construction of ademe.

I have found by mathematical calculation and by actual experiments that in the curve ot' a perfect arch of equipollence, be the superincumbent static load upon the arch what it may, the length of the ahscissa at any point in such curve is invariably equivalent to the load at such point multiplied by the leverage (from the skewback) and the product divided by the maximum thrust. It is therefore only requisite to find the lengths of the abs'cisste, or of a sufficient number thereof for practical purposes, iu order to be able to obtain the proper curve of the arch in each special case.

I shall first demonstrate my method of determining the correct form for such an arch of even load.

Upon a base, U N, Fig. 3, equalin length to one-half that ofthe span or chord ofthe proposed arch, I erect a right-angled triangle, A G N, whose altitude, A C, is equal to the rise or IOO versed sine of said arch. In the present illustration the whole span is taken as twenty feet, the rise at ten feet, the gure (3) being to scale of one-half inch to the foot. The Weight above and resting upon the points A Al A2, &c.-ten in all, let it be supposed of the hypotenuse A N is represented by the unit l, whether one pound or one ton is immaterial. Now, bearingin mind the rule above stated, I will show, as an example, how the proper length for the fifth abscissa risin gfrom thepoint G5 is obtained. The entire load upon the hypotenuse is 10. The maximum thrust at A is therefore 5. The proportion of weight upon A5 is 7.5, which multiplied by 5, the leverage from N, (the skewback of the proposed arch,) gives a product of 37.5; this divided by 5, the maximum thrust, gives a quotient ot' 7.5 feet as the correct length of the abscissa B5 G5 for the true arch of equipollence of equal load. A similar calculation, startingfrom any other point in the hypotenuse AN, will determine the length of the abscissa of the arch passing through such point. Thus the arch Z, ot' even load, having the thrust the same at every pointtherein, is laid down by drawing a line, A Z N, connecting the summits ofthe several abscissae B B2, 8vo. The figures in the plane of the Z arrow represent the lengths ot' ten of the abscissze of this arch.

I shall now proceed to show the application of my said method in the determination of the form of an arch, Y, of equipollence in the case ofuuequalload, the chord and rise ofthe arch bein g assumed as of the samelength, respectively, as before. The space contained by the straight lines F A N E, Fig. 3, is presumed to be filled in with earth or other material of the specific gravity of that which shall be over the arch after it is built. Say, for instance, that this mass of material below the line F E of the road or street, supported by the hypotenuse A N, weighs onev hundred and tit'ty pounds to the foot. A simple. calculation, which I do not deemit necessary to enter into here, gives flve thousand pounds as the theoretical maximum thrust at the point A. Now, taking for illustrationv the weight or load sustained at the point A5, which is found to be.8,125.75, and multiplying the same by they leverage, live feet, the product 40,628.75 results, and this, divided by the maximum thrust, 5,000, gives 8.12-i-feet-the proper length of the abscissa D5 C5 of the true arch Y (in this case) of equipollence. By repeating the foregoing calculation with suitable change of factors required by the rule hereinbefore stated, based from as many other .points in hypotenuse A N' as may be thought advisable, the respective abscissa-lengths may be obtained. The lengths of several of the abscissae of arch Y are given in a line opposite the Y arrow, Fig. 3. It is obvious that the greater number of abscissa-lengths thus found the more nearly the curve will approach the theoretically-perfect arch of cquipollence for the special case. Ordinarily it is necessary to determine the lengths of but afew-of such abscissae. If, however, the work to be constructed is of much magnitude or importance, it is desirable to attain a greater degree ot' accuracy in the curve of the arch by calculating the lengths of a comparatively large number of abscissae.

The curveX, Fig. 3, is that of a semicirculax` arch of the same span and rise as the true arch Y under' the same circumstances. vThis is the most usual f orm of arches for sewers and manyother purposes. The difference between these curves X and Y in the present instance indicates obviously a large quantity of matef rial of the arch built upon the former out of line. In long sewers or conduits the economy in labor and material secured in the construe tion of my arch over the semicircular or Roman arch is very considerable. The curve of equipollence of the arch', under the special circumstances, having been thus substantiallydetermined, I now construct a corresponding .templet, T, of wood or other suitable material,

such as is shown in'Figs. 1 and 2. This is mounted upon a bed or frame, L, and is provided with a series of platform-steps, P, upon which the masons are supported while building the arch H. AThe structure is adapted to be easily moved forward horizontally, as desired, upon wheels W, fitted to run upon' rails R, which are suitably laid in the line of the intended conduit. In the present instance these rest upon a cross,,picce,(),thrown across the lower section ofthe conduit. The wheels and rails may, however, be dispensed with, and the device be made to-slide upon ways tixed at the sides, or upon the bottom ot' the interior of the conduit, or otherwise.

In building long arches, as for sewers, conracked up, as seen in Fig. l. At the beginning of the arch H, for a short distance, the templet T performs the function ot1 a center or support for the material being laid-that is, until the bricks are racked upon each side, near to the crown of the arch, and the crown- IOO IOS

duits, &c., the arch-bricks or voussoirs are i bricks (or keystones) have been driven in place, whereupon thearch springs slightly outcase, of using the usual rigid centers, which a are left in place until the mortar or cement between the voussoirs of the superstructure shall have hardened and the earth or other material be filled in above the arch. Although such arch be designed to carry an uneven load, and built before the load actually comes upon it, yet it will stand, under almost all circumstances', without adventitious support., for the reason that practically the true curve of the arch ofequipollence of even load will generally lie somewhere between the intrados and the back of such arch of uneven load. If, however, as in extreme cases, the character ofthe superincumbentload which is to rest upon the completed arch is such as to demand-a curve so far from that of the arch of equipollence of even load that there may be danger of the unloaded archfalling in, I lay upon the main arch H, Fig.2, a 1re-enforcing rib or course, J at suitable intervals. I also employ such re-enforcing ribs in long arches-such as for sewers-in order to counteract the relative weakness due to the length of such structures, for the longer they are the weaker they are with the same thickness of materialthroughout. l prefer to locate one of said ribs, which need be but two or three feet broad under ordinary cir-A -cumstances,opposite each house along the route ofthe sewer, sothatconnections between thelatter and the house-mains may be made through the re-enforcement, thusavoiding or counteracting the weakening of the main arch, which would otherwise result. Such re-enforcing ribs serve also to arrest the damage which might be caused by careless or unskillful workmen in building the sewer.

In constructing domes I first determine the proper outline of a suitable templet according to the principles of the system hereinbefore elucidatedpthe effect ot' the lantern, if any, which is to crown the dome, being taken into account in arriving at the several abscissa lengths ofthe arch of the dome. I then construct a templet,lT, such as shown in Fig. 4. It is provided with a rib, G, of the desired contour, on its exterior edge, and is fixed upon a fra me or platform, I, having wheels W,where by the templet may be rotated upon a center, K, around the circle of the dome in process of construction, from time to time, as may be necessary, as the work of building proceeds. Instead of a single one, several such templetri bs, supported upon frame I, may be used where a number of masons are at work at as many points in the circumference of the circle ofthe dome; also, in lieu of such templet, a revolvingtinger, devised so that it lnay be swept around and give the proper line upon which to build the dome, may be employed.

A dome constructed according to the principles of my system needs no support while bc-v ing built. 1

I claim- 1A. The improvement in the art of' constructing arches, consisting in racking up the bricks against a center or support at the beginning, and then proceeding by racking up in close proximity to a movable templet, the latter heing shifted forward from time to time during the process of building .the arch, substantially as and for the purpose set forth.

2. The improved method of constructing an arch of equipollence, consisting in racking up the bricks upon a movable templet at the beginning', as upon a center, till near the crown; then driving in the crown bricks, thereby springing the arch outslightly from thetemplet; then successively moving the templet forward as the arch is further laid up without bearing upon the templet, substantially as described.

3. Theprocessofconstructinganarch,which consists in laying the bricks up against a templet or center until near the crown, and then springing out the arch by forcing in the crown-bricks, thus freeing the arch from the center, substantially as described.

4. In the construction of arches accordingto the manner or process hereinbefore described, a non-collapsing templet upon guides or ways, and adapted to be gradually shiftcdvwhile the arch is in process ot' construction, substantially as and for the purposes set forth.

5. rlhe movable templet T, provided with platform-steps P, substantially as and for the purposes shown and described.

6. Intheconstructionofarches,the voussoirs arranged in curvilinear form, in combination with an ununiform static load located above said voussoirs and supported thereon, said arch being without supporting abutments above its springing points or skewbacks, and having but two resultants which pass down through the slrewbacks, substantially as and for the purpose specified.`

7. An arch, in combination with an unevenly-distributed static load, said arch having but two resultante, coinciding with the lineof curvilinear pressure, the abscissa at anypoint ot' said arch being equal to the gravity-press ure or static load multiplied by the leverage thereof and divided by the curvilinear press ure or estimated maximum thrust, as set forth.

THOMAS J. LOVEGROVE.

WTitn esses J osEPH M. NAGLEE, JOHN BURKHARDT.

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